✨ Add support for gif NFT images

Runtime/Plugins/Unity-GifDecoder/Decode/GifBitBlockReader.cs

@@ -0,0 +1,114 @@
+using System.IO;
+using ThreeDISevenZeroR.UnityGifDecoder.Utils;
+
+namespace ThreeDISevenZeroR.UnityGifDecoder
+{
+    /// <summary>
+    /// Reader for GIF Blocks
+    /// </summary>
+    public class GifBitBlockReader
+    {
+        private Stream stream;
+        private int currentByte;
+        private int currentBitPosition;
+        private int currentBufferPosition;
+        private int currentBufferSize;
+        private bool endReached;
+        private readonly byte[] buffer;
+
+        public GifBitBlockReader()
+        {
+            buffer = new byte[256];
+        }
+
+        public GifBitBlockReader(Stream stream) : this()
+        {
+            SetStream(stream);
+        }
+
+        /// <summary>
+        /// Set new stream
+        /// </summary>
+        public void SetStream(Stream stream)
+        {
+            this.stream = stream;
+        }
+
+        /// <summary>
+        /// Read first block and initialize reading
+        /// </summary>
+        public void StartNewReading()
+        {
+            currentByte = 0;
+            currentBitPosition = 8;
+            ReadNextBlock();
+        }
+
+        /// <summary>
+        /// Skips to the last block, if end is not reached
+        /// </summary>
+        public void FinishReading()
+        {
+            while (!endReached)
+            {
+                ReadNextBlock();
+            }
+        }
+
+        /// <summary>
+        /// Read bits from stream and construct value
+        /// </summary>
+        /// <param name="count">Bit count to read</param>
+        /// <returns>Value from readed bits</returns>
+        public int ReadBits(int count)
+        {
+            var result = 0;
+            var bitsToRead = count;
+            var offset = 0;
+            var bitsAvailable = 8 - currentBitPosition;
+
+            while(bitsToRead > 0)
+            {
+                if (currentBitPosition >= 8)
+                {
+                    currentBitPosition = 0;
+                    bitsAvailable = 8;
+
+                    if (endReached)
+                    {
+                        // Some gifs can read slightly past end of a stream
+                        // (since there is a zero byte afterwards anyway, it is safe to return 0)
+                        currentByte = 0;
+                    }
+                    else
+                    {
+                        currentByte = buffer[currentBufferPosition++];
+                        if (currentBufferPosition == currentBufferSize)
+                            ReadNextBlock();
+                    }
+                }
+
+                var mask = (byte) (((1 << bitsToRead) - 1) << currentBitPosition);
+                var readCount = bitsAvailable < bitsToRead ? bitsAvailable : bitsToRead;
+
+                result += ((mask & currentByte) >> currentBitPosition) << offset;
+
+                currentBitPosition += readCount;
+                bitsToRead -= readCount;
+                offset += readCount;
+            }
+
+            return result;
+        }
+
+        private void ReadNextBlock()
+        {
+            currentBufferSize = stream.ReadByte8();
+            currentBufferPosition = 0;
+            endReached = currentBufferSize == 0;
+
+            if(!endReached)
+                stream.Read(buffer, 0, currentBufferSize);
+        }
+    }
+}